enh: store basic software info in png metadata

yt/funcs.py

@@ -18,7 +18,7 @@
 from copy import deepcopy
 from functools import lru_cache, wraps
 from numbers import Number as numeric_type
-from typing import Any, Callable, Optional, Type
+from typing import Any, Callable, Dict, Optional, Type
 
 import numpy as np
 from more_itertools import always_iterable, collapse, first
@@ -565,8 +565,10 @@ def get_yt_version():
 def get_version_stack():
     import matplotlib
 
+    from yt._version import __version__ as yt_version
+
     version_info = {}
-    version_info["yt"] = get_yt_version()
+    version_info["yt"] = yt_version
     version_info["numpy"] = np.version.version
     version_info["matplotlib"] = matplotlib.__version__
     return version_info
@@ -1447,3 +1449,24 @@ def validate_moment(moment, weight_field):
             "Weighted projections can only be made of averages "
             "(moment = 1) or standard deviations (moment = 2)!"
         )
+
+
+def setdefault_mpl_metadata(save_kwargs: Dict[str, Any], name: str) -> None:
+    """
+    Set a default Software metadata entry for use with Matplotlib outputs.
+    """
+    _, ext = os.path.splitext(name.lower())
+    if ext in (".eps", ".ps", ".svg", ".pdf"):
+        key = "Creator"
+    elif ext == ".png":
+        key = "Software"
+    else:
+        return
+    default_software = (
+        "Matplotlib version{matplotlib}, https://matplotlib.org|NumPy-{numpy}|yt-{yt}"
+    ).format(**get_version_stack())
+
+    if "metadata" in save_kwargs:
+        save_kwargs["metadata"].setdefault(key, default_software)
+    else:
+        save_kwargs["metadata"] = {key: default_software}

yt/utilities/png_writer.py

@@ -1,10 +1,18 @@
 from io import BytesIO
 
+import PIL
 from PIL import Image
+from PIL.PngImagePlugin import PngInfo
+
+from .._version import __version__ as yt_version
 
 
 def call_png_write_png(buffer, fileobj, dpi):
-    Image.fromarray(buffer).save(fileobj, dpi=(dpi, dpi), format="png")
+    metadata = PngInfo()
+    metadata.add_text("Software", f"PIL-{PIL.__version__}|yt-{yt_version}")
+    Image.fromarray(buffer).save(
+        fileobj, dpi=(dpi, dpi), format="png", pnginfo=metadata
+    )
 
 
 def write_png(buffer, filename, dpi=100):

yt/visualization/base_plot_types.py

@@ -8,7 +8,13 @@
 import numpy as np
 from matplotlib.ticker import LogFormatterMathtext
 
-from yt.funcs import get_interactivity, is_sequence, matplotlib_style_context, mylog
+from yt.funcs import (
+    get_interactivity,
+    is_sequence,
+    matplotlib_style_context,
+    mylog,
+    setdefault_mpl_metadata,
+)
 from yt.visualization._handlers import ColorbarHandler, NormHandler
 
 from ._commons import (
@@ -162,6 +168,7 @@ def save(self, name, mpl_kwargs=None, canvas=None):
             mpl_kwargs = {}
 
         name = validate_image_name(name)
+        setdefault_mpl_metadata(mpl_kwargs, name)
 
         try:
             canvas = get_canvas(self.figure, name)

yt/visualization/tests/test_save.py

@@ -2,6 +2,7 @@
 import re
 
 import pytest
+from PIL import Image
 
 import yt
 from yt.testing import fake_amr_ds
@@ -23,6 +24,16 @@ def test_save_to_path(simple_sliceplot, tmp_path):
     assert len(list((tmp_path).glob("*.png"))) == 1
 
 
+def test_metadata(simple_sliceplot, tmp_path):
+    simple_sliceplot.save(tmp_path / "ala.png")
+    with Image.open(tmp_path / "ala.png") as img:
+        assert "Software" in img.info
+        assert "yt-" in img.info["Software"]
+    simple_sliceplot.save(tmp_path / "ala.pdf")
+    with open(tmp_path / "ala.pdf", "rb") as f:
+        assert b"|yt-" in f.read()
+
+
 def test_save_to_missing_path(simple_sliceplot, tmp_path):
     # the missing layer should be created
     p = simple_sliceplot